1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine and a printer, having a function of forming an image on a recording material such as a sheet.
2. Description of the Related Art
Conventionally, as an image forming apparatus such as a copying machine and a laser beam printer, an image forming apparatus using an intermediate transfer member is known. In such image forming apparatus, a plurality of photosensitive drums is arranged in parallel in contact with the intermediate transfer member, and a primary transfer process and a secondary transfer process form a color image (multicolor image) on a recording material.
In the primary transfer process, a toner image formed on a surface of the photosensitive drum is transferred onto the intermediate transfer member. The primary transfer process is performed on each of toner images in a plurality of colors to superimpose and transfer the toner images therein onto the surface of the intermediate transfer member. In the secondary transfer process to be sequentially performed, the toner images in the plurality of colors formed on the surface of intermediate transfer member are collectively transferred at a secondary transfer position onto a surface of the recording material fed from a cassette. At this point, after the recording material fed from the cassette temporarily waits at a predetermined position just before the secondary transfer position, it is re-fed in association with the timing when the toner image on the intermediate transfer member reaches the secondary transfer position.
To reduce a production cost, some image forming apparatuses do not provide a recording material size detection mechanism for cassettes.
In this case, as performing a print operation, an image forming apparatus detects an actual length of a recording material (hereinafter, referred to as a “recording material length”) in a conveyance direction of the recording material. After the detection, based on the detection result of the length of the recording material, the print operation is controlled. More specifically, for example, Japanese Patent Application Laid-Open No. 2008-122935 discusses the image forming apparatus in which the print operation is performed at an image forming interval and a paper feeding interval of the recording material appropriate for the detection result of the length of the recording material.
For the image forming apparatus, a throughput is generally defined based on an A4 size (referred to as “A4”, hereinafter) in a product catalog, and, in some cases, even for the A4 or smaller recording material, the throughput may be designed not to exceed (to be the same as) the throughput for A4 sheet printing. Therefore, when the printing is performed on the recording material smaller than A4, it is performed with the same throughput as that for A4. The throughput herein refers to the number of images to be formed per unit time.
As described above, print control is performed in an order of feeding, stopping, and re-feeding the recording material. In the control, a required time from starting to feed to starting to re-feed the recording material may be extended. Its cause may be slip of the recording material in a paper feeding operation when the recording material is being fed, and a conveyance trouble due to abrasion of a roller for conveying the recording material. In consideration of delay of the conveyance of the recording material due to various types of causes, if the feeding is started earlier before re-feeding timing, even if the delay occurs, the recording material can be possibly conveyed in time. When the small-size recording material is specified, as described above, the control is conventionally performed with the throughput equivalent to that for A4. In other words, the image is formed at the same image forming interval as that for A4 sheet printing and, according to the image forming interval, the feeding interval is determined. As a result, the paper-feeding timing is the same as that for A4 sheet printing. In other words, for example, for A5 size (referred to as “A5”, hereinafter) sheet printing, a subsequent recording material is not fed right after a previous recording material has been fed, but the recording material is fed after the A4 interval has elapsed. Thus, the feeding timing is delayed for the size of the recording material.